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High-resolution four-wave-mixing spectroscopy of collision-induced narrow resonances in Doppler-broadened systems

1988; American Institute of Physics; Volume: 38; Issue: 9 Linguagem: Inglês

10.1103/physreva.38.4639

0556-2791

Jing Liu, D. G. Steel,

Cold Atom Physics and Bose-Einstein Condensates

We report a series of measurements of the nearly degenerate four-wave-mixing response in atomic sodium in the presence of a helium buffer gas. The results show the line shape associated with both the ground-state and excited-state dynamics. The line shape evolves as a function of pressure from a dip at a pressure of 0 Torr to a spike at a few Torr due to the presence of collisions. The width of the spike is determined by residual Doppler broadening. At higher pressure (\ensuremath{\ge}10 Torr), the width of the spike is further narrowed below the residual Doppler width. The additional reduction is due to a form of Dicke narrowing associated with the dynamics of the lower- and upper-level excitations. The results are in qualitative agreement with a perturbation solution of the density-matrix equations which include the effects of velocity-changing collisions and state-changing collisions.